Present day technique resorts chiefly as concerns the field of ramjets to the heat energy obtained by transforming under permanent operative conditions the potential energy of fuel inside a combustion chamber through which a gasiform current flows at a clearly subsonic speed, corresponding for instance to a Mach number equal to 0.15 at a maximum. The conditions governing the combustion and its propagation have a deflagrating character and the stabilisation of the flame (in the case where the components of the combustive mixture have been mixed beforehand) or that of the reaction area (that is of the diffusion flame in the case of a direct injection of fuel) is obtained by producing inside the gasiform stream a macroturbulence obtained by mechanical means.
The possibilities of obtaining such combustion chambers working under subsonic conditions are limited, on the one hand by the large size of the chambers which are necessary by reason of the low speed of flow of the gasiform stream and by the necessary expansion of the reaction area wherein a deflagrating combustion is produced, and on the other hand by the maximum temperatures allowable, which depend on the characteristic thermic resistance of the material forming the mechanical means with which the flame is necessarily in contact.
It is true that it is possible, as well-known in the art, to produce and maintain a detonating or substantially detonating combustion within a gasiform stream flowing permanently at a supersonic speed, practically at a Mach number equal to or about about 1.2 provided said combustion is stabilized by means of a shock wave stabilized in its turn inside the supersonic stream. A combustion chamber of such a type has been described for instance in the French Pat. No. 1 008 660 which shows how a stable shock wave may be obtained by the impact of a gasiform stream flowing at a supersonic speed against a hindrance constituted for instance by the leading edge of a diffuser. The shock wave thus obtained is in the shape of a surface extending transversely of the direction of the stream and supported by the hindrance which has produced it. Thus, the combustion area is necessarily in contact with the structural member forming the hindrance of which the resistance against heat limits the maximum allowable temperature, which may be reached during combustion.